Recent tendency of semiconductor devices having more minute patterns requires an increasing level of accuracy for measuring by a semiconductor dimension-measuring apparatus to measure dimensions of the patterns. Especially a demand for accuracy to reduce instrumental errors in dimension-measurement values among measuring apparatuses has become tighter year by year.
A semiconductor dimension-measuring apparatus is configured to irradiate a sample as an observation/measurement target with a focused electron beam for two-dimensionally scanning on the sample plane, obtain a scanning electron microscope (SEM) image based on detected secondary electrons generated from the irradiated sample, and designate a measurement portion of a pattern dimension on the SEM image, thus calculating the pattern dimensions for measurement using a detected signal waveform of the corresponding portion based on the magnification of the SEM image.
Meanwhile, in the case of a charged particle beam apparatus like a semiconductor dimension-measuring apparatus to acquire an SEM image, i.e., a charged particle beam image, when an electron beam as a charged particle beam for image acquisition is incident obliquely on a sample, the resultant charged particle beam image of the sample will change with the incident angle of the charged particle beam to the sample, i.e., the landing angle of the charged particle beam. In this case, the landing angle of a charged particle beam refers to the angle between the normal line of the sample and the beam optical axis of the charged particle beam.
In this way, since a dimension is measured using a semiconductor dimension-measurement apparatus based on an SEM image as stated above, the SEM image obtained will change with the incident angle of the electron beam to the sample even for measurement of dimensions of the same sample having the same pattern, and so the measurement value of the pattern dimension will change. Then, a semiconductor dimension-measurement apparatus is designed so that, when an electron beam is not deflected intentionally, the electron beam is incident on the sample plane having a pattern therein vertically to acquire an SEM image.
However, there are no techniques available for a charged particle beam apparatus including a semiconductor dimension-measurement apparatus to measure 0.1° or less of minute inclination angle of a charged particle beam that is defined by the optical axis of the charged particle optical system to deflect and focus the charged particle beam and the beam optical axis of the charged particle beam that is deflected by this charged particle optical system. This leads to a failure to check actually whether the electron beam is incident vertically on the sample plane or not along the optical axis direction of the electronic optical system that deflects and focuses the electron beam even when the electron beam is not deflected intentionally as stated above. This means that, even when the electron beam, i.e., the charged particle beam is not deflected, a minute inclination of the charged particle beam occurs in each apparatus with respect to the optical axis of the electron optical system, i.e., the charged particle optical system, and the amount of such an inclination varies from one apparatus to another, and so there is an instrumental error that is a difference in dimensions measured among apparatuses due to this minute inclination.
Meanwhile, a conventionally available method to correct an inclination angle of the electron beam, i.e., the charged particle beam is to use a sample with a polyhedral structure having a known shape, e.g., a pyramid pattern having a known shape, formed therein as a calibration pattern as described in Patent Literature 1. Then, an SEM image of the pyramid pattern as the calibration pattern is acquired, the incident angle of the charged particle beam with respect to the sample when acquiring this SEM image, i.e., the landing angle of the charged particle beam is estimated based on a geometric deformation of the pyramid pattern on this SEM image, and inclination angle of the charged particle beam corresponding to each landing angle with respect to the sample is corrected based on the thus estimated landing angle.
FIG. 9 describes a pyramid pattern as one example of the calibration pattern. FIG. 9(a) schematically shows the three-dimensional shape of the pyramid pattern, and FIG. 9(b) shows an SEM image of the pyramid pattern part of the sample in which the pyramid pattern shown in FIG. 9(a) is formed.
In FIG. 9(a), the pyramid pattern 90 is formed with a square pyramid-shaped concave pattern having a (111) plane that is exposed by crystal anisotropy etching of a silicon (Si) wafer and three planes having a crystal plane orientation equal to this (111) plane. Thus, angles formed by the planes of such a pyramid pattern 90 are known. In the drawing, P0 to P4 represent apexes of the pyramid, where the apex P0 corresponds to the bottom apex of the pyramid pattern 90 and the apexes P1 to P4 correspond to corners at the opening part of the pyramid pattern 90. The planes P0P1P2, P0P2P4, P0P4P3 and P0P3P1 of the pyramid pattern 90 have inclination angle with respect to the (100) plane of silicon as the wafer plane that is tan−1(√2)≈54.74°.
The pyramid pattern 90 as the calibration pattern may be a square pyramid-shaped convex pattern instead of the square pyramid-shaped concave pattern. The pattern shape itself of the polyhedral structure also is not limited to the square pyramid shape (pyramid shape) as shown in the drawing, which may be pyramid frustum shaped, for example.
As shown in FIG. 9(b), on a top-down SEM image 900 (SEM image acquired by observing a wafer plane with the pyramid pattern 90 formed therein from the vertically above in the illustrated example) of the pyramid pattern 90 shown in FIG. 9(a), four valley lines of the pyramid pattern 90 are straight lines P0P1, P0P2, P0P3 and P0P4 connecting the apex P0 and the remaining apexes P1 to P4 based on a change of the values of detected signal, and the opening part of the pyramid pattern 90 appears as intersecting lines of the planes P0P1P2, P0P2P4, P0P4P3 and P0P3P1 of the pyramid pattern 90 with the wafer plane, i.e., line segments P1P2, P2P4, P4P3 and P3P1.
Then Patent Literature 1 describes a method of acquiring an SEM image by observing a sample with the pyramid pattern having a known shape formed therein from a predetermined desired observation direction, estimating incident angle of an electron beam with respect to the sample at that time based on a geometric deformation of the pyramid pattern on the SEM image, and adjusting the deflection of the electron beam, for example, so that the estimated incident angle becomes the setting value corresponding to the set desired observation direction, thus bringing the inclination angle of the electron beam to the observation direction of the sample.
Patent Literature 2 describes a method of acquiring an SEM image of a polyhedral pattern part of a sample with the polyhedral pattern having a known shape formed therein and estimating incident angle of an electron beam with respect to the sample based on a geometric deformation of the polyhedral pattern on the SEM image using the technique described in Patent Literature 1, while acquiring an SEM image of the polyhedral pattern part of the same sample as that is used for the estimation in another apparatus as well, and estimating incident angle of an electron beam with respect to the sample based on a geometric deformation of the polyhedral pattern on the SEM, whereby their incident angles of the electron beams are associated so that the incident angles of the electron beams with respect to the sample can be made to coincide with each other among the apparatuses, thus correcting an instrumental error that is a difference in dimension measured among the apparatuses due to differences in incident angle of the electron beam among the apparatuses.